Characterization of Arabidopsis thaliana SMC1 and SMC3:: evidence that AtSMC3 may function beyond chromosome cohesion

Structural maintenance of chromosome (SMC) proteins are conserved in most prokaryotes and all eukaryotes examined. SMC proteins participate in many different aspects of chromosome folding and dynamics. They play essential roles in complexes that are responsible for sister chromatid cohesion, chromosome condensation and DNA repair. As part of studies to better understand SMC proteins and sister chromatid cohesion in plants we have characterized Arabidopsis SMC1 and SMC3. Although transcripts for AtSMC1 and AtSMC3 are present throughout the plant, transcript levels for the two genes vary between different tissues. Cell fractionation and immunolocalization results showed that AtSMC3 was present in the nucleus and cytoplasm. In the nucleus, it is primarily associated with the nuclear matrix during interphase and with chromatin from prophase through anaphase in both somatic and meiotic cells. During mitosis and meiosis the protein also co-localized with the spindle from metaphase to telophase. The distribution of AtSMC3 in syn1 mutant plants indicated that SYN1 is required for the proper binding of AtSMC3 to meiotic chromosomes, but not the spindle. Data presented here represent the first detailed cytological study of a plant SMC protein and suggest that SMC3 may have multiple functions in plants.